Hydrocarbons, and in particular petroleum, are produced from the ground as a mixture. This mixture is converted to useful products through separation and processing of the streams in reactors. The conversion of the hydrocarbon streams to useful products is often through a catalytic process in a reactor. The catalysts can be solid or liquid, and can comprise catalytic materials on a support. In particular, catalytic metals on a support are extensively used. The catalytic metals include platinum group metals, as well as other metals. During the processing of the hydrocarbons, the catalysts deactivate over time. One primary cause of deactivation is the generation and buildup of coke on the catalyst. The accumulation of coke blocks access to catalytic sites on the catalyst. The regeneration of the catalyst is normally performed through the removal of the coke, where the coke is combusted at a high-temperature with a gas having oxygen. These processes can be performed either in a continuous manner with the catalyst cycled through the reactor and the regenerator, or the process can be performed in a semi-continuous manner, such as with multiple fixed beds, where one bed is taken off stream to regenerate the catalyst, while the other beds continue operation.
With the continuous regeneration process, a recycle gas is continuously passed to the combustion zone in the regenerator and a flue gas containing the combustion products is removed. The combustion process is controlled through the oxygen content in the recycle gas. The recycle gas stream comprises a portion of the flue gas, and an additional stream of new combustion gas, while venting another portion of the flue gas from the regenerator. This helps maintain the temperature of the combustion gas, as well as setting up a steady state condition of continuous addition of spent catalyst and combustion gas to the regenerator, while continuously drawing regenerated catalyst and flue gas.
Catalyst regeneration methods are disclosed in U.S. Pat. No. 5,053,371 to Williamson, and U.S. Pat. No. 6,048,814 to Capelle, et al. for removing coke from catalyst particles through combustion. The combustion process can be damaging to the catalyst, and better methods of control of the combustion process are important for improving the life of the catalyst in the reactor-regenerator cycle. Producing a better process allows for more cycles of the catalyst through the regenerator, and increases the life of the catalyst. This can be achieved through improvements in the process and control of the regenerator.